Comparison of linear and nonlinear regression for modeling the first-order degradation of pest-control substances in soil

First-order kinetic models are often used to profile the degradation of pest-control compounds in soil. This approach is based on enzyme theory and is often favored due to its simplicity and its requirement by regulatory agencies. Here, linear and nonlinear regression approaches to modeling first-order decay are compared. Composite residual plots of many soil degradation data sets are presented on a normalized scale. These plots illustrate the general error structure for the data and are useful for detecting common mis-specifications of the models. Results indicate that a nonlinear regression approach to modeling first-order decay of compounds in soil more accurately describes most data sets when compared with a linear approach. Specifically, the observed error structure does not support the broad use of a logarithmic transformation to stabilize the variance. In addition, models generated using the linear approach generally exhibit more dramatic systematic deviations from the observations as compared with models generated using the nonlinear approach. The analysis methods described here may be useful for comparing alternative models in this and other research areas.     

Effects of water exchange and abiotic factors on zooplankton and epibenthic fauna in shrimp ponds

Assemblages of zooplankton and epibenthic invertebrates were collected from a commercial Penaeus monodon (Fabricius) pond at fortnightly intervals over an entire grow‐out season. The pond inlet and outlet water were also sampled intensively over three 1‐week periods throughout the season. Before stocking the ponds with shrimp postlarvae, copepods dominated the zooplankton. Immediately after the ponds were stocked, there was a rapid decline in zooplankton numbers, particularly the dominant larger copepods, suggesting heavy predation by shrimp postlarvae. For the rest of the season, barnacle nauplii were the dominant zooplankton component in the pond. Pond water exchanges had little detectable influence on the composition or density of the zooplankton assemblage. Instead, the dominance of barnacle nauplii appeared to have been maintained by steady recruitment due to barnacle reproduction in the pond. While changes in the biomass of pond zooplankton were not correlated with physico‐chemical characteristics, changes in density were positively correlated with temperature, and negatively correlated with pH, dissolved oxygen and secchi disc readings. Epibenthic faunal density peaked at the end of the season, while the biomass peaked during the middle part of the season. Sergestids (Acetes sibogae Hansen) were the most abundant epibenthic taxa. No correlations were found between physico‐chemical parameters and epibenthic fauna biomass or density. Abundances of epibenthic fauna were not related to zooplankton densities, suggesting that trophic interactions between these assemblages is not important. No Acetes were captured in samples of outlet water, and only on a single occasion were large numbers captured in the inlet water; after this, there was a notable increase in the number of Acetes in the pond. This evidence, together with the lack of an increase in the size of Acetes during the season, suggests that water exchange is an important but unpredictable source of recruitment of epibenthic fauna into the pond. The results emphasize the benefits of ensuring that appropriate zooplankton assemblages have been introduced into the ponds, when they are filled, to support the shrimp immediately after stocking. This will depend on the initial inoculum and may be difficult to manipulate with water exchanges once established. Assemblages of epibenthic fauna appear more likely to change with exchanges and may need to be monitored across the season, particularly if their presence reduces production through adverse impacts such as competition with postlarvae, introduction of disease or deteriorated water quality.     

Saharan dust and the atmospheric inputs of elements and alkalinity to mediterranean ecosystems

Saharan dust delivered by so-called ‘red rains’ strongly influences precipitation chemistry in the Mediterranean region. We show here that at rural sites in eastern Spain, red rains have much higher ion concentrations than non-red rains, and they account for up to 50% of the mean annual input of dissolved elements in bulk precipitation, though they make up only a minor part of the annual rainfall. The mean annual input of alkalinity in red rains is enough to neutralize the input of free acidity in acidic precipitation. Transport of Saharan dust is thus a major ecological force in Mediterranean ecosystems through its effects on the acid neutralizing capacity of the atmosphere and the atmospheric deposition of elements.     

Transport of Escherichia coli and F-RNA Bacteriophages in a 5-M Column of Saturated, Heterogeneous Gravel

The relative transport and attenuation of bacteria, bacteriophages, and bromide was determined in a 5?m long?×?0.3?m diameter column of saturated, heterogeneous gravel. The average pore velocity (V), longitudinal dispersivity (?? _x ), and total removal rate (??) were derived from the breakthrough curves at 1, 3, and 5?m, at a flow rate of 24.8?L?h^?1. The experiments largely confirmed the differences in transport and attenuation patterns among bacteria, phages, and bromide, and between colloid-associated and ??free?? microorganisms, previously observed in a study using homogeneous pea gravel. Cultured Escherichia coli J6-2 cells were transported faster than phage MS2 and bromide, consistent with velocity enhancement of the larger particles. The evidence for velocity enhancement of phage MS2 compared with bromide was less conclusive, with some evidence of retardation of the phage as a result of adsorption?Cdesorption processes in the finer media. On average, phage in sewage and adsorbed to kaolin particles were transported faster than free phage, suggesting that most sewage phage are adsorbed to colloids. However, average velocities of cultured and sewage E. coli differed far less, suggesting that most E. coli in sewage exist as individual (non colloid-associated) cells. There was no conclusive evidence that the wider pore size range in the heterogeneous mixture compared with pea gravel increased velocity enhancement effects. Removal rates of free phage were far higher than in the pea gravel, and were attributed to adsorption in the finer materials. Equivalent increases in removal of cultured and sewage E. coli and colloid-associated phage were attributed to straining in finer materials and settling in quiescent zones. Inactivation (??) rates (determined in the pea gravel study) indicated little contribution to removal of either free or attached microorganisms. The results showed the importance of association with colloids in determining the relative transport of bacteria and viruses in alluvial gravels.     

Phenotypic variation in progenies from somatic hybrids between Brassica napus and Sinapis alba

A number of variant phenotypes, such as long siliques, high density of pods, increased seed number per pod and yellow seed color resembling Sinapis alba, were selected from intergeneric somatic hybrids between Brassica napus and Sinapis alba through successive backcrosses. Resistance to Sclerotinia sclerotiorum among 24 BCF₄ lines was also tested by inoculation with mycelia, and four lines showed stronger resistance than the resistant rapeseed variety ‘Zhongshuang 9’. Comparative anatomy studies on mature seed revealed that the seed coat pigments were mainly distributed in the palisade layer, which is considerably thinner in S. alba compared to B. napus. The area index of protein bodies in cotyledon cells was highest in S. alba, lowest in B. napus and intermediate in the intergeneric progenies. This study demonstrates that wide hybridization can enable exploitation of valuable trait diversity from S. alba for broadening the genetic basis for rapeseed breeding.     

Effect of stem guying on the incidence of resin pockets

Although resin pockets are a major cause of degrade for appearance grade timber, little is known about the environmental conditions that control the incidence of these defects. Water stress and mechanical bending stress due to tree sway in strong winds are thought to contribute to the formation of resin pockets, but this is based on anecdotal evidence from observations of resin pocket occurrence. Controlled experiments are required to better understand the factors leading to resin pocket formation.     

Linking future population food requirements for health with local production in Waterloo Region,Canada

Regional planning for improved agricultural capacity to supply produce, legumes, and whole grains has the potential to improve population health as well as the local food economy. This case study of Waterloo Region (WR), Canada, had two objectives. First, we estimate the quantity of locally grown vegetables, fruits, legumes, and whole grains needed to help meet the Region of Waterloo population’s optimal nutritional requirements currently and in 2026. Secondly, we estimate how much of these healthy food requirements for the WR population could realistically be produced through local agriculture by the year 2026. Results show that a shift of approximately 10% of currently cropped hectares to the production of key nutritious foods would be both agriculturally feasible and nutritionally significant to the growing population. We supplement our findings with some agronomic considerations and community-level strategies that would inform and support such change. The methodology of this study could be applied to other regions: more such analyses would create a broader picture of the diverse qualitative and quantitative agricultural shifts that could synchronize optimal land use with dietary recommendations, thus informing coordinated policy and planning.